Infinitely adjustable engagement system and method

ABSTRACT

A system for releasable engagement of two bodies where one of the bodies deforms the other body during the engagement process. The system includes a first body having an engagement surface that is made from a pseudo-elastic mater pseudo-elastic material is maintained at an operating temperature that is above the martensite-austenite transition temperature for the material. The second body has an indenter surface that contacts the pseudo-elastic material and exerts sufficient stress to convert the material from the relatively hard austenite state to the relatively soft martensite state wherein the material conforms to the indenter shape. Upon release of the indenter contact stress, the pseudo-elastic material changes back to its original shape.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to systems and methods for engaging twobodies together. More particularly, the invention involves theengagement of two bodies where, during the engagement process, one ofthe bodies deforms the other body.

2. Description of Related Art

Clamping mechanisms are used for a variety of purposes including linearmotors. One conventionally used clamping design includes locking surfaceteeth. While this arrangement can support large lateral forces, thedistance between the teeth limits step size. Althoughmicro-electromechanical system (MEMS) technology is helpful, teethspacing reduction is limited, limiting step size and utility for highprecision applications. Stepping speed is also significant, and ensuringproper teeth meshing for each step is often problematic, especially athigh stepping frequencies. If teeth fail to mesh properly, damage andwear can occur, significantly reducing the effectiveness of a clampingdevice. Similarly, in gearing mechanisms, two mating gears must havecorrect pitch, or damage can occur. In mechanical designs, such astransmissions, two gears with dissimilar pitch often require engagement,requiring additional gears, added cost, added complexity, added weight,increased use of belts, and can cause slipping and shorten the life ofgears.

U.S. Pat. No. 5,810,881 issued to Hoskin, et al. describes a clampingdevice that penetrates into a titanium nickel alloy. A shape memoryalloy is described such that heating of the material causes a phasetransformation. However, since heating is required, it is an inherentlyslow process. Such heating also requires the use of added devices, mass,adding complexity and cost.

U.S. Pat. No. 5,226,683 issued to Julien et al. describes a sealinggasket utilizing nickel and titanium. While deformation forces aredescribed, recovery of the gasket upon removal of the clamping force isrequired. Further, a smooth surface is desired for the seal and thesurfaces that contact the seal. Also, again, heating of the seal isdescribed.

SUMMARY OF THE INVENTION

In accordance with the present invention, systems and methods areprovided for releasable engagement of two bodies. The systems include afirst body that has an engagement surface that is designed forengagement with the indenter surface of the second body. As a feature ofthe present invention, the engagement surface of the first body is madefrom a pseudo-elastic material that is maintained at an “operatingtemperature”. The operating temperature is above themartensite-austenite transition temperature of the pseudo-elasticmaterial such that the pseudo-elastic material undergoes a conversionbetween the relatively hard austenite state and the relatively softmartensite state during application of stress (pressure) by theindenter. As a result, the engagement surface conforms to the indentersurface that includes one or more teeth. The penetration of the indenterteeth into the first body provides a secure and precise engagement ofthe two bodies.

The system includes an engagement mechanism that positions the twobodies relative to each other and provides reversible contact of theindenter surface with the engagement surface. When the indenter teethare withdrawn from contact with the engagement surface (stress removed),the pseudo-elastic material returns to the austenite state and theengagement surface returns to its original unstressed shape. The twobodies may then be repositioned and the engagement process repeated. Asa feature of the present invention, the return of the engagement surfaceto its original shape allows one to make extremely small movementsduring repositioning of the two bodies prior to re-engagement.Accordingly, the system essentially provides for an infinite degree ofposition adjustments.

The systems and methods of the present invention are particularly usefulfor engagement systems where precise positioning and/or rapid engagementand re-engagement of two bodies is required. High frequency engagementis possible because heat is not required to convert the pseudo-elasticengagement surface back to its original (non-deformed) shape. Thesystems and methods are well suited for use in micro systems where theindenter teeth and pseudo-elastic engagement surfaces are extremelysmall and capable of positioning the two engagement bodies withprecision in the sub-micron range.

In addition, the use of a pseudo-elastic material provides wearresistance that increases the life of clamping or gearing mechanisms, ascompared to conventional designs. Further, the invention can be utilizedin gearing systems where gears (indenters) of different pitch mustinteract with a single gear (engagement surface).

The above discussed and many other features and attendant advantages ofthe present invention will become better understood by reference to thedetailed description when taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A)-(C) are partially diagrammatic cross-sectional views thatdemonstrate the engagement of a first and second body in accordance withthe present invention. FIG. 1(A) shows the initial configuration of thebodies prior to engagement. FIG. 1(B) shows the two bodies engaged. FIG.1(C) shows the two bodies after they have been disengaged.

FIG. 2 is a partially diagrammatic cross-sectional view illustrating anexemplary embodiment of the present invention where the indenter (secondbody) is surrounded by the first body (pseudo-elastic material. The twobodies are shown disengaged.

FIG. 3 is a partially diagrammatic cross-sectional view illustrating anexemplary embodiment of the present invention where the first body(pseudo-elastic material) is surrounded by the indenter (second body).The two bodies are also shown disengaged.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments are described with reference to specificconfigurations. Those of ordinary skill in the art will appreciate thatvarious changes and modifications can be made while remaining within thescope of the appended claims. Additionally, well-known elements,materials, devices, components, methods, process steps and the like maynot be set forth in detail in order to avoid obscuring the invention.

The systems and methods of the present invention may be used in a widevariety of applications where precise and secure engagement of two ormore bodies is required. The invention may be used in connection withlinear motors (stepper, DC brushed and brushless servo, inductance andAC synchronous, etc.), gearing systems, clamping systems,medical/surgical applications, dental applications, eyeglassapplications, optical applications, precision placement applications andvarious other applications requiring fast-acting, high holding force,infinite step size resolution clamping. For example, the invention maybe applied to positioning or to positioning optical systems over longtravel with high resolution.

The invention is also useful in high frequency engagement-disengagementapplications where high operational speeds are required. Where speed ofoperation is less important (i.e. optical positioning), the systems andmethods of the present invention may be used to provide very small andprecise changes in engagement positions. The invention is also useful inclamping systems where a fast-acting, high holding force, infinite stepsize resolution clamping device is required. The invention is applicableto situations and systems where one of the bodies is a drive orpositioning gear. The invention provides for low-wear/long life gearswith infinite pitch and an infintely precise engagement mechanism. Theinvention is well suited for use in linear motors to where it provideshigh power density, low complexity and low cost.

An exemplary engagement system in accordance with the present inventionis shown at 10 in FIG. 1 (A). The system 10 is shown in the disengagedposition. The system 10 includes a first body 12 and a second body 14.The system 10 further includes an engagement mechanism that is showndiagrammatically at 16. The engagement mechanism can be any of the knownmechanisms that are capable of orienting and engaging the two bodies 12and 14 together with sufficient force to provide the desired phasechange in the first body as will be described in detail below. A backingplate or substrate 13 is provided to support the first body 12, ifdesired. The substrate 13 is optional and may be deleted if it is notnecessary or required for a particular system configuration orparticular pseudo-elastic material.

The engagement mechanism 16 typically includes a control unit 18 andmechanical elements represented by lines 20 and 22 that are designed toorient the two bodies 12 and 14 relative to each other and to engage anddisengage the two bodies 12 and 14 under the control of the control unit18. Exemplary engagement mechanisms include linear step motors, clampingmechanisms and gear engagement-disengagement mechanisms, such astransmissions and drive units. The engagement mechanism can be as simpleas a screw or scissors type clamp that is manually or electronicallyoperated to engage the two bodies or it may be as complex as amulti-element engagement system, such as a precision linear step motorsystem that precisely engages the two bodies together at differentprecise locations.

The first body 12 has an engagement surface 24. The first body 12 ismade from a pseudo-elastic material. Suitable pseudo-elastic materialsare those that undergo a phase transition from the martensite state tothe austenite state at a temperature (the A_(f) temperature) that isabove the operating temperature of the first body 12. The “operatingtemperature” of the first body is the temperature at which the firstbody is maintained during the engagement and disengagement process. Theoperating temperature for the first body 12 in engagement systems inaccordance with the present invention can vary from cryogenictemperatures up to 400° C. and above. The operating temperature that isselected for a particular system will depend upon the A_(f) temperatureof the particular pseudo-elastic material that is used. Operatingtemperatures on the order of room temperature up to 300° C. arepreferred.

As used herein, the term A_(f) refers to the temperature at which analloy finishes transforming from the martensite state to the austenitestate when the material is not under stress (i.e. at atmosphericconditions). Those skilled in the art will appreciate that when thepseudo-elastic material that makes up first body 12 is at an operatingtemperature that is above its A_(f), applied stress lowers the elasticstrain energy and induces an austenite to martensite transformation.When the stress is removed, the transformed martensite reverts back tothe austenite phase, providing shape recovery. That is, thepseudoelastic material recovers its shape, not upon the application ofheat, but upon a reduction of stress.

It is also known that the amount of stress that must be applied toinduce the austenite to matensite transformation increases as thedifference between the operating temperature and the A_(f) of thepseudo-elastic material increases. Accordingly, it is preferred that theoperating temperature of first body 12 be maintained within 40° C. ofthe Af temperature for a given pseudo-elastic material during theengagement and disengagement process. It is particularly preferred thatthe operating temperature be within 30° C. of A_(f). When the operatingtemperature is more than 40° C. above the Af, the amount of pressure(stress) that must be used to transform the pseudo-elastic material to amartensite state becomes prohibitive. In general, the stress or pressurethat must be applied to achieve the transition from austenite tomartensite will range from 30 mpa for operating temperatures close toA_(f) up to 500 mpa for operating temperatures that are closer to thepreferred 40° C. upper limit.

Any of the known pseudo-elastic materials may be used to form first body12. Exemplary pseudo-elastic materials include nickel-titanium alloys,nickel-titanium-copper alloys, copper-based alloys, platinum alloys,palladium alloys, hafnium alloys, gallium alloys and cadmium alloys.Exemplary alloys include nickel-titanium-platinum,nickel-titanium-palladium, nickel-magnesium-gallium, gold-cadmium andnickel-titanium-hafnium.

Nickel-platinum alloys are preferred that contain 50 atom percent nickeland 50 atom percent titanium. Nickel-titanium alloys with other atompercentages are suitable including those that include 51 atom percentnickel and 49 atom percent titanium. A preferred operating range fornickel-titanium alloys (50/50) is from 100 to 130° C.

The engagement surface 24 may be any shape. It can be planar ornon-planar. For example, the engagement surface can be arcuate,cylindrical, spherical or flat (planar). The first body 12 can also beany size or thickness. Preferably, the first body 12 will have athickness (t) on the order of a few millimeters down to a few angstroms.

The second body 14 (also referred to as an “indenter”) has an indentersurface 26 that is in the form of teeth 28. Each tooth 28 has a base 30with a cross-sectional area and a tip 32. The shape and dimensions ofthe teeth 28 may vary widely depending upon the particular engagementsystem. The cross-sectional area of the base 30 will preferably rangefrom a few square millimeters down to one square micron and below. Thedistance from the tip 32 of each tooth to the base 30 is preferably froma few millimeters to a few nanometers and below. The teeth 28 may be inthe form of ridges having a rectangular cross-section, triangularcross-section, circular cross-section, truncated triangularcross-section (as shown in FIG. 1(A)). The teeth may also be in the formof individual indenters such as pyramids, truncated pyramids, cylinders,spheres and irregular shaped protrusions.

The second body 14 is made from a material that is capable of/designedto apply force and increase stress on the pseudo-elastic material at theengagement surface 24. The indenter or second body 14 can be made fromany material that is harder than the pseudo-elastic material in themartensite state. Preferably, the indenter material is also harder thanthe pseudo-elastic material when it is in the austenite state. Exemplaryindenter materials include steel and steel alloys as well as silicon.

In FIG. 1(B), the engagement system 10 is shown in the engaged positionwhere mechanical elements 29 and 22 have exerted enough stress(pressure), as indicated by arrowheads 21 and 23, to convert the firstbody 12 from an unloaded body (austenite state) as shown at 12 in FIG.1(A) to a loaded body (martensite state) as shown at 12 a in FIG. 1(B).During the engagement process, the engagement surface is converted froman unstressed shape 24 (FIG. 1(A)) to a stressed shape 24 a (FIG. 1(B)).The first body 12 a is sufficiently soft in the martensite state that itconforms to or matches the shape of the indenter teeth as they arepressed into the first body 12. This deformation of the unstressedengagement surface 24 to the stressed engagement surface 24 a providesfor a secure engagement of the two bodies.

The indenter teeth penetrate and lock into the pseudo-elastic material.This penetration into the pseudo-elastic material increases the supportof lateral loads, as compared to a conventionally used, material undersimilar stress.

FIG. 1(C) shows the engagement system after it has been disengaged fromthe engaged position shown in FIG. 1(B). During unloading, the indentersurface 26 and engagement surface 24 are retracted from each other(removing stress from the pseudo-elastic material). The pseudo-elasticmaterial reverts back to an austenite phase providing shape recovery asshown at 24 c. Recovery of the deformation of the pseudo-elasticmaterial is accomplished when stress is removed, due to the compositionof pseudo-elastic material. Recovery of the pseudo-elastic materialoccurs without heating due to the release of stress (pressure) thatallows the material to revert back to the austenite state. As shown bythe horizontal arrows in FIG. 1(C), the first body 12 and second body 14may be moved relative to each other to a different position from thatshown in FIG. 1(A). Since the first body 12 has returned to its originalshape, the position of the two bodies relative to each other prior tore-engagement can be infinitely adjusted. As a result, the engagementmechanism 10 is capable of infinite step resolution.

The invention may be used in clamping systems where the first and secondbodies are clamped together (engaged) and unclamped (disengaged) at aspeed/frequency range of 0.01 to 100,000 hertz (Hz). The invention isparticularly well suited for use in clamping devices that operate athigh operational speeds of 10,000 Hz and above. As used herein, theoperational speed refers to the loading (indenting) and unloading(removing stress). It is to be appreciated that the loading andunloading can occur repeatedly. It is also to be appreciated thatbetween loading and unloading, indenter (second body) 14 and/or thepseudo-elastic material (first body) 12 may be repositioned. Theinvention may also be used for long term (quasi-static) engagement, ifdesired, where the operational speed approaches 0.0 Hz. In addition, thesupport or substrate 13 may be deleted, if necessary, in systemsoperating at high operational speeds.

An alternate embodiment of an engagement system in accordance with theinvention is shown in partial diagrammatic form at 40 in FIG. 2. Thesystem is shown in the disengaged position. The system 40 includes twonon-planar first bodies 42 and 43 that surround a rod-shaped second body44. The first bodies 42 and 43 each have engagement surfaces 46 and 47,respectively, that engage the indenter teeth 48. The indenter teeth 48are in the form of triangular ridges. The first bodies 42 and 43 aremade form pseudo-elastic material as previously described and the secondbody is made from an appropriate indenter material. The two first bodies42 and 43 are maintained at the appropriate operating temperature forthe particular pseudo-elastic material being used.

The system 40 includes a control unit 50 that operates clampingmechanisms 52 and 54 to provide clamping and unclamping of the first andsecond bodies as represented by arrows 56 and 58, respectively. Thefirst body is shown as two arcuate halves that are displaced from eachother a sufficient distance to allow the engagement surfaces 46 and 47to be moved into contact with the indenter teeth. However, the firstbody may be in the form of a single cylindrical body that surrounds theindenter provided that the material is sufficiently flexible to beforced into contact with the indenter. In addition, the support orsubstrate shown in FIG. 1 has been deleted from the embodiment shown inFIG. 2. If desired, an arcuate support for one or both of the firstbodies 42 and 43 may be used.

Another alternate embodiment of an engagement system in accordance withthe invention is shown in partial diagrammatic form at 60 in FIG. 3. Thesystem 60 is also shown in the disengaged (unclamped) position. Thesystem is the same as system 40 except that the first body 62 isrod-shaped and the second body is in the form of two arcuate clamps 64and 65. The arcuate clamps 64 and 65 also have triangular shaped ridges66 and 67, respectively, that function as indenter teeth. The indenterteeth are clamped down on the first body engagement surface 68 to applythe necessary stress to convert the pseudo-elastic material fromaustenite state to the martensite state with the resultant penetrationof the teeth into the pseudo-elastic engagement surface. The clampingand unclamping of the clamps 64 and 65 is accomplished usingconventional clamping mechanisms as represented by lines 70 and 72 ascontrolled by control unit 74. It should be noted that the entire rod 68does not have to be made from pseudo-elastic material. It is onlynecessary that the engagement surface 68 include a layer ofpseudo-elastic material that is sufficiently thick to accommodate thedepth of penetration by the indenter teeth.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the present invention.Accordingly, the present invention is not limited to the above preferredembodiments and examples, but is only limited by the following claims.

1. A system for releasable engagement of two bodies, said apparatuscomprising: a first body comprising an engagement surface, saidengagement surface comprising a pseudo-elastic material, saidpseudo-elastic material being at an operating temperature, saidoperating temperature being above the martensite-austenite transitiontemperature for said pseudo-elastic material, said pseudo-elasticmaterial being capable of conversion between an austenite state and amartensite state by application of stress to said first body at saidengagement surface, said application of stress to said engagementsurface thereby converting said first body from an unloaded body to aloaded body wherein the engagement surface of said unloaded body has anunstressed shape and the engagement surface of said loaded body has astressed shape wherein said stressed shape is different from saidunstressed shape; a second body comprising an indenter surface forcontacting the engagement surface of said first body, said indentersurface being formed by one or more teeth that extend from said secondbody for engagement with said first body, said second body comprising amaterial that is harder than said pseudo-elastic material in saidmartensite state; and an engagement mechanism that provides reversiblecontact of said indenter surface with said engagement surface andprovides for the application of sufficient stress to said engagementsurface to provide reversible conversion of said engagement surface fromsaid unstressed shape to said stressed shape wherein said stressed shapeconforms to the shape of said indenter teeth.
 2. A system for releasableengagement of two bodies according to claim 1 wherein said operatingtemperature is within 40° C. above said martensite-austenite transitiontemperature.
 3. A system for releasable engagement of two bodiesaccording to claim 1 wherein said operating temperature is between roomtemperature and 300° C.
 4. A system for releasable engagement of twobodies according to claim 1 wherein in said engagement surface of saidfirst body is non-planar.
 5. A system for releasable engagement of twobodies according to claim 4 wherein said engagement surface surroundssaid indenter body.
 6. A system for releasable engagement of two bodiesaccording to claim 4 wherein said said indenter body surrounds saidengagement surface.
 7. A system for releasable engagement of two bodiesaccording to claim 1 wherein said indenter body is a gear.
 8. A systemfor releasable engagement of two bodies according to claim 7 whereinsaid engagement mechanism comprises a linear motor.
 9. A system forreleasable engagement of two bodies according to claim 1 wherein saidengagement mechanism comprises a clamping apparatus for clamping saidfirst and second bodies together.
 10. A method for engaging anddisengaging two bodies, said method comprising the steps of: providing afirst body comprising an engagement surface, said engagement surfacecomprising a pseudo-elastic material, said pseudo-elastic material beingat an operating temperature, said operating temperature being above themartensite-austenite transition temperature for said pseudo-elasticmaterial, said pseudo-elastic material being capable of conversionbetween an austenite state and a martensite state by application ofstress to said first body at said engagement surface, said applicationof stress to said engagement surface thereby converting said first bodyfrom an unloaded body to a loaded body wherein the engagement surface ofsaid unloaded body has an unstressed shape and the engagement surface ofsaid loaded body has a stressed shape wherein said stressed shape isdifferent from said unstressed shape; providing a second body comprisingan indenter surface for contacting the engagement surface of said firstbody, said indenter surface being formed by one or more teeth thatextend from said second body for engagement with said first body, saidsecond body comprising a material that is harder than saidpseudo-elastic material in said martensite state; contacting saidindenter surface with said engagement surface to apply sufficient stressto said engagement surface to convert said engagement surface from saidunstressed shape to said stressed shape wherein said stressed shapeconforms to the shape of said indenter teeth; and removing said indentersurface from contact with said engagement surface to thereby providereturn of said engagement surface to said unstressed shape.
 11. A methodfor engaging and disengaging two bodies according to claim 10 thatincludes the additional steps of: moving said first and second bodiesrelative to each other after the step of removing said indenter surfacefrom contact with said engagement surface to thereby providerepositioned first and second bodies; and contacting said indentersurface with said engagement surface of said repositioned first andsecond bodies to apply sufficient stress to said engagement surface toconvert the engagement surface of said repositioned bodies from saidunstressed shape to said stressed shape wherein said stressed shapeconforms to the shape of said indenter teeth.
 12. A method for engagingand disengaging two bodies according to claim 10 wherein said operatingtemperature is within 40° C. above said martensite-austenite transitiontemperature.
 13. A method for engaging and disengaging two bodiesaccording to claim 10 wherein said operating temperature is between roomtemperature and 300° C.
 14. A method for engaging and disengaging twobodies according to claim 10 wherein in said engagement surface of saidfirst body is non-planar.
 15. A method for engaging and disengaging twobodies according to claim 14 wherein said engagement surface surroundssaid indenter body.
 16. A method for engaging and disengaging two bodiesaccording to claim 14 wherein said indenter body surrounds saidengagement surface.
 17. A method for engaging and disengaging two bodiesaccording to claim 10 wherein said indenter body is a gear.
 18. A methodfor engaging and disengaging two bodies according to claim 17 whereinsaid engagement mechanism comprises a linear motor.
 20. A method forengaging and disengaging two bodies according to claim 12 wherein saidengagement mechanism comprises a clamping apparatus for clamping saidfirst and second bodies together.